As diesel emission requirements become more stringent, vehicle and engine manufacturers are forced to develop and implement diesel emission improvement strategies. The current effort is focused around reducing particulate matter, hydrocarbons and carbon monoxide while trying not to increase nitrogen oxide emissions. Engine and fuel technology can only reduce these emissions to a certain point; beyond this ancillary systems are required to meet emission regulations set by world-wide governing bodies.
One emission technology that is employed is the coupling of a diesel oxidation catalyst and a diesel particulate filter. The diesel oxidation catalyst removes up to 90% of hydrocarbons and carbon monoxide and 10% of particulate matter. The diesel particulate filter is used to remove up to 95% of particulate matter. A diesel particulate filter must be operated at high temperatures to convert the particulate matter into less harmful constituents. If the diesel particulate filter temperature is too low, its capacity becomes finite and vehicle performance will become inhibited as a result of the increase in exhaust backpressure. The diesel particulate filter runs at a relatively high temperature of approximately 450 to 700° C. to initiate self regeneration. Operating under these conditions gives the diesel particulate filter an infinite capacity. To maintain the high diesel particulate filter temperature, it is important that the diesel oxidation catalyst operate at the high temperature as well as the close packaging of the two passive devices to reduce thermal losses. The diesel oxidation catalyst temperature is engine load dependant, therefore diesel oxidation catalyst/diesel particulate filter temperature may not always be at an optimum temperature for continuous diesel particulate filter regeneration.